A TDD frame structure in a long term evolution (LTE) system is shown in FIG. 1. In such frame structure, a 10 ms radio frame is divided into two half-frames, each of which is divided into ten time slots equally of a length of 0.5 ms, and every two time slots forms a 1 ms sub-frame, thus the radio frame includes ten sub-frames (numbered from 0 to 9) and the radio frame includes twenty time slots (numbered from 0 to 19). For a normal cyclic prefix (CP) of a length of 5.21 us and 4.69 us, one time slot includes seven uplink/downlink symbols equally of a length of 66.7 us, wherein the cyclic prefix length of the first symbol is 5.21 us, and the cyclic prefix length of each of other six symbols is 4.69 us; for an extended cyclic prefix of a length of 16.67 us, one time slot includes six uplink/downlink symbols. Additionally, in such frame structure, the configuration of the sub-frame possesses features as following.
Sub-frame 0 and sub-frame 5 are fixedly used for downlink transmission.
Uplink/downlink switching with a period of 5 ms and 10 ms is supported.
Sub-frame 1 and sub-frame 6 are special sub-frames, which are used to transmit three special time slots that are a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS), wherein,
the DwPTS is used for downlink transmission;
the GP is guard time, and is not used to transmit any data; and
UpPTS is used for uplink transmission, at least including 2 uplink single carrier-frequency division multiple access (SC-FDMA) symbols, which are used to transmit physical random access channels (PRACH).
When the uplink/downlink switching with a period of 5 ms is implemented, sub-frame 2 and sub-frame 6 are fixedly used for uplink transmission.
When the uplink/downlink switching with a period of 10 ms is implemented, the DwPTS is present in two half-frames, the GP and the UpPTS are present in the first half-frame, the length of the DwPTS in the second half-frame is 1 ms, and sub-frame 2 is used for uplink transmission, sub-frame 7 to sub-frame 9 are used for downlink transmission.
Primary-synchronization (P-SCH) signals are sent in the first orthogonal frequency division multiplexing (OFDM) symbol of the DwPTS; and secondary-synchronization (S-SCH) signals are sent in the last OFDM symbols of time slot 1 and time slot 11.
Pilots of the first and second antennas are sent in the first OFDM symbol and on the third OFDM symbol from the last in a time slot, and pilots of the third and forth antennas are sent in the second OFDM symbol in a time slot.
In view of that the P-SCH signal sending on the first OFDM symbol of the DwPTS interferes with the original pilot sending of the first and second antennas, it is required to redesign the pilot in the DwPTS, which will result in increase of system complexity.